1. Field of the Invention
The invention is related to an ultrasonic imaging device for clinical use in medicine. More specifically, the invention is related to a means for electronically simulating the rotating prism used in many conventional ultrasonic scanning devices.
2. Description of Prior Art
In recent years considerable activity has taken place to develop and produce rapidly-scanned ultrasonic imaging devices for clinical use in medicine. Such devices typically operate at megahertz frequencies and can be electronically focused and scanned. Generally, such devices use either ultrasonic or charge-coupled diode delay lines to provide the necessary phasing and time delay for focusing and scanning arrays of ultrasonic transducers. Conventional systems using such devices include B-type sectoral and raster scanners that are completely electronic in nature and a variety of C-type scanners. In the latter case the simplest system is a linear array that focuses and scans in one dimension and may be translated transversely by a mechanical motion in order to provide a two-dimensional image. More elaborate conventional systems consist of two orthogonally crossed linear arrays of the type described above, one array used as a transmitter and the other as a receiver in a transmission system scanned in two dimensions. This provides fully electronic two-dimensional scanning, with only 2 N transducer elements needed for N.sup.2 resolvable spots. However, it is inefficient in that only the power at the intersection point of the two cylindrically focused beams is used for constructing the image. Even more elaborate conventional systems are possible consisting of two-dimensional arrays of transducers and capable of providing a spherically focused beam scanned in two dimensions over the C-plane. Such systems have the disadvantage of requiring complex mechanical arrays to provide a spinning prism, multiple delay lines, complex electromechanical interconnections and, generally, a double mixing process.
The instant invention avoids these disadvantages and limitations of the prior art by providing an electronically simulated rotating ultrasonic prism having an electronically variable focal length. This device provides a system capability for electronically scanning a spherically focused beam in a C-scan mode using a spiral path rather than a traditional raster pattern. The instant invention has no fragile rotating prism; requires only a single delay line; has very simple electromechanical interconnections; and does not require multiple mixing.